1. Technical Field
The present invention relates to a microelectromechanical system (MEMS) switch structure and, more particularly, to a CMOS (complementary metal-oxide-semiconductor)-MEMS switch structure featuring integration of CMOS and MEMS technologies.
2. Description of Related Art
A switch for use in a telecommunication system must have high isolation and low insertion loss to prevent the system from noise interference and maintain system performance. Mechanical switches, for example, are preferred in telecommunication systems where high-frequency operation is required. Besides, as it is generally required that switches in a telecommunication system be more and more compact and lightweight, CMOS-MEMS switches which feature total compatibility with CMOS manufacturing processes have been developed.
Typically, a CMOS-MEMS switch incorporating both CMOS and MEMS manufacturing processes is made by first performing a standard CMOS manufacturing process, then defining the desired MEMS element areas with a photoresist, and releasing the defined MEMS elements by etching. However, as the major metal used in the CMOS manufacturing process is aluminum, which tends to oxidize and become an electrically insulating aluminum oxide when exposed to air, the surface electrodes of the resultant CMOS-MEMS switch elements may contact each other without effectively making electrical connection therebetween.
Please refer to FIG. 1 for a schematic drawing of a conventional CMOS-MEMS switch structure 100 configured to be closed (i.e., turned on) by lateral contact between surface electrodes 122 and 142 on the cantilever beams 12 and 14, wherein the cantilever beams 12 and 14 serve as a contact switch in the CMOS-MEMS switch structure 100. When making the lateral contact-based CMOS-MEMS switch structure 100, the line width limitations of existing MEMS manufacturing processes prevents the two opposing ends of the cantilever beams 12 and 14 from being in close proximity. As a result, it is difficult for the surface electrode 122 on the top surface of the cantilever beam 12 and the surface electrode 142 on the top surface of the cantilever beam 14 to make electrical contact with each other. Moreover, if the cantilever beams 12 and 14 have such a poor structural design that both cantilever beams bend upward, the distance between the aforesaid two ends of the cantilever beams 12 and 14 will be further increased. Therefore, the manufacture of the lateral contact-based CMOS-MEMS switch structure 100 still has many problems to be solved.